#-*-coding:utf-8-*-

from decimal import Decimal
import math

def main():
    x1,y1,x2,y2 = map(Decimal,input().split())
    print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2)))

if __name__=="__main__":
    main() from decimal import Decimal import math math def main():
    x1,y1,x2,y2 = map(Decimal,input().split())
    print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2))) main x1,y1,x2,y2 = map(Decimal,input().split()) x1 map(Decimal,input().split()) map Decimal input().split() ().split () input split y1 x2 y2 print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2))) print "{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2)) "{:.8f}".format "{:.8f}" format math.sqrt((x2-x1)**2+(y2-y1)**2) math.sqrt math sqrt (x2-x1)**2+(y2-y1)**2 (x2-x1)**2 x2-x1 x2 x1 2 (y2-y1)**2 y2-y1 y2 y1 2 if __name__=="__main__":
    main() __name__=="__main__" __name__ "__main__" main() main def main():
    x1,y1,x2,y2 = map(Decimal,input().split())
    print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2))) def main():
    x1,y1,x2,y2 = map(Decimal,input().split())
    print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2))) main
#-*-coding:utf-8-*-

from decimal import Decimal
import math

def main():
    x1,y1,x2,y2 = map(Decimal,input().split())
    print("{:.8f}".format(math.sqrt((x2-x1)**2+(y2-y1)**2)))

if __name__=="__main__":
    main()
